Lime Neutralization of Industrial Wastewater Without Slaking

Eastman Chemical Company's wastewater treatment facility receives an average flow of 29 million gallons per day of low pH wastewater. The combination of organic acids and mineral acids causes the pH to average 5.0 and requires neutralization before the wastewater enters the activated sludge process. This wastewater must be treated with a neutralizing additive. The additive used at Eastman Chemical Company is calcium oxide or dry lime. Neutralization of the wastewater is the first stage of the treatment process. When the current treatment facility was constructed in 1988, it was equipped with a neutralization process that included two lime slakers and twelve rotodip liquid feeders. Each slaker was equipped with a grit removal screen that would remove inert solids from the slaker. High maintenance and repair costs for the slakers and rotodip liquid feeders combined with the frequent and excessive need for operator attention led the staff to explore alternative methods of neutralization. A first step was to replace the pebble lime with powdered lime, which allowed for the elimination of the grit removal screens. The powdered lime reduced a number of the operational problems. The lime vendor had also suggested that an added benefit was that the powdered lime might not require the slaking process because of the short time required to dissolve into calcium hydroxide. The possibility of eliminating maintenance problems in the lime system was very appealing and led to a search of an alternative system that did not include slakers or rotodip liquid feeders. An eductor-control valve system was developed. After a couple of modifications in design, a system was developed that significantly reduced maintenance and repair costs and provided improved control of the lime concentration and feed rate. This alternative system was installed by 1999, which resulted in a maintenance cost savings of about 50,000 per year.